Contemporary activity of colistin and polymyxin B against a worldwide collection of Gram-negative pathogens: Results from the SENTRY antimicrobial surveillance program (2006-09)

Abstract

Objectives: To comparatively evaluate the antimicrobial activities of colistin and polymyxin B with those of other antimicrobials against a worldwide collection of 40625 Gram-negative bacilli. Methods: Antimicrobial susceptibility testing was performed and interpreted using the CLSI broth microdilution method except for colistin against Enterobacteriaceae. Results: The polymyxins showed potent in vitro activities (MIC90, ≤0.5-1 mg/L) against this large collection of clinical isolates, with very low resistance rates (<0.1%-1.5%). Resistance to the polymyxins remained stable among organisms tested except for Klebsiella spp. isolates collected from the Asia-Pacific and Latin American regions, where a trend towards greater resistance was observed (P≤0.05). In addition, an important reduction in imipenem susceptibility among Acinetobacter spp. and Klebsiella spp. was demonstrated in most geographical regions. Conclusions: Although the polymyxins showed excellent in vitro activity against the vast majority of Gramnegative bacilli evaluated, a trend to greater resistance was observed in the Asia-Pacific and Latin American regions. Therefore, the clinical use of polymyxins must be cautious and surveillance monitored. © The Author 2011. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.